To lose one world heritage site is unfortunate, to lose four catastrophic. But that is the prospect facing the United Kingdom – Unesco's advisers are recommending that three sites should be described as "endangered", in addition to Liverpool's waterfront, which already has this label. There is every likelihood that Unesco will follow this advice. Designation as endangered is one step away from removal from the list altogether, a fate which has so far befallen only two of the 962 in the world.

The three sites are the Palace of Westminster and its environs, Hayle Harbour in Cornwall, and the Giant's Causeway in Antrim. As we reveal in other pages today, all are threatened by commercial development – office and residential towers near Westminster, a supermarket in Hayle, and a golf course near the Giant's Causeway – which the government has shown no wish to limit.

This is not the result of carelessness, but of deliberate, if underpublicised, policy. The communities secretary Eric Pickles is consistently choosing not to use his powers to call in controversial proposals for planning inquiries. These include the Liverpool Waters development that put the city's waterfront on the endangered list, the Hayle supermarket, and the tall building proposals in Waterloo and Vauxhall that are threatening Westminster's status. At the same time bodies such as English Heritage and the Commission for Architecture and the Built Environment, whose role is to raise the standard of new development and protect existing places, have been weakened.

The government's National Planning Policy Framework contains phrases which loosen previous planning protections. For example, listed buildings can be destroyed "in order to achieve substantial public benefits". The evidence of Pickles's decisions, as when waving through the demolition of the Edwardian Jessop hospital in Sheffield, is that this provision can be interpreted broadly. The government also wants to enlarge the domestic extensions that can be built without planning permission, and only modified these policies when it was pointed out that they could cause strife between neighbours.

This is not just a matter of individual cases, but of large-scale and permanent effects across the country. Large infrastructural projects such as HS2 are being proposed, and the expansion of wind farms and fracking. The government wants, though so far with little success, to boost house building. This makes the question of planning – how much do we want, of what kind and for whom? – critical.

The government's position is that almost nothing should get in the way of growth. Planning is an obstruction to be minimised. And it is a reasonable question to ask, whether existing controls are the right ones, or worth their costs, or achieving their supposed ends. But what is lacking from their view is a positive idea of what planning can achieve.

Planning should be about the balance of values – heritage, jobs, beauty, business, individuals. It should prevent damage to long-term assets (such as world heritage sites) to achieve short-term benefits (such as building flats to attract speculative overseas investors), but it should also make sure that shared benefits, like public transport and renewable energy, are not unreasonably obstructed by individual interests.

It should not only say where development can't happen, but identify places where it can. It can direct development for better rather than worse. A thousand new houses can be planned so that they use land well and create good new places to live, or they can be smeared thoughtlessly across the landscape.

It should also provide clarity, not least for economic reasons. Take Elizabeth House, the tower at Waterloo which is provoking many of Unesco's worries: the site's owners have been pushing for a tower here for a decade. It was obvious at the start that a tall building here would impact on Parliament Square, and no architectural genius could make it smaller. In a good planning system there would have been a clear answer at the outset, as to whether it was acceptable. Instead, there was a maybe, which has led to millions spent on abortive projects and 10 years of inaction.

In other words, intelligent planning becomes more important if wind power, high-speed trains and new homes are wanted. Instead, the government weakens planning, belatedly adapting its position when it provokes vociferous opposition. Last week it announced that communities will receive more money from wind farms in their area, and that they will have a greater say, but not exactly a veto, over them. Again, there is vagueness, which suits no one.

The engagement of people affected by development is desirable, and is part of the government's localism agenda, but it is insufficient on its own. The weakness of localism is that it assumes that citizens have the skills, knowledge and time to engage with complex planning issues when often they do not. This can expose them to greater risk of exploitation by undesirable development, not less.

If public opinions are the only constraining factor, the result is a kind of economic conflict. When planning is weak, it favours people with the resources to fight for their back yards – the groups that can hire lawyers, run campaigns and organise publicity. It means in practice that poorer areas, no matter how scenic, will find it harder to resist proposals. Large-scale construction will go not where it best fits a place, but where local people are most desperate for a bung. This can be seen in Hayle, where the supermarket is being presented as the only way to pay for maintenance of the harbour.

It is never fashionable to support planning. It conjures images of robotic officials, of faceless bureaucrats telling people what's good for them. Planners do, and will always, make mistakes. They can never please everyone, and planning should never be immune from reform. But for all that, the British planning system has done a reasonably good job, over the decades, of protecting landscapes and historic buildings, without turning the whole country into a frozen-in-aspic theme park of pre-industrial rusticity.

This year is the centenary of the Ancient Monuments Act, which first introduced that statutory protection – "listing" – of historic buildings. It is embarrassing, and shameful, that, at the same time, Unesco might single out the United Kingdom for its shoddy treatment of some of its most important landmarks. And the issue is about more than monuments – it is about the environments in which everyone lives, and treating them with respect and care.